| 研究課題/領域番号 |
15H05211
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| 研究機関 | 名古屋大学 |
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研究代表者 |
WALLIS R・Simon 名古屋大学, 環境学研究科, 教授 (30263065)
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| 研究分担者 |
鷺谷 威 名古屋大学, 減災連携研究センター, 教授 (50362299)
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| 研究期間 (年度) |
2015-04-01 – 2018-03-31
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| キーワード | Bolivia / Uyuni / Lake shorelines / Tufa / Age / Neo tectonics |
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| 研究実績の概要 |
We undertook a second field survey around the Uyuni basin including kinematic GPS measurements of lake shorelines and sampling of associated tufa and volcanic units. We expanded the area of study to include the less well studied Coipasa basin to the north of the main Uyuni salt flats. We sampled both lake tufa and lesser amounts of volcanic rock. Microscopic studies show the tufa has little organic material and is highly porous. In addition its development as finds to boulders or within crevasses suggests that it originated due to wave agitation of the upper water levels releasing CO2 and reducing the pH of the lake water. We can therefore exclude the possibility that the lake tufa formed as bioherms some depth below the water line or as chimneys related to meteoric water seepage. The height of the tufa can therefore be used as an indication of former lake level. We carried out dating of tufa samples: 23 samples by 14C dating and 12 samples by U-series dating. The volcanic rocks can potentially be used 10Be dating that can reveal the exposure time and can also be related to the time at which lake level dropped sufficiently to expose the rock surface. One sample of quartz-rich material was selected for a trial measurement.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
We have largely completed the measurements of shoreline heights and taken sufficient samples to obtain a good overall idea of the ages. The final year of research will include a short trip to Uyuni to complete a small number of measurements in key areas and to collect a limited number of new samples for radiometric dating. We will also attempt to examine the lateral extent of shorelines by using areal survey techniques. These activities can be completed in the time available. The final aspect is to perform the mechanical modelling required to examine possible causes of shoreline distortion. This will be undertaken in the next few months before we leave for the next field season. Overall the research is on target to be complete by the end of this academic year we therefore consider it to be progressing as planned.
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| 今後の研究の推進方策 |
The research carried out in Bolivia has given us a good understanding of how to examine similar areas in other parts of the world. We will revisit the work that we undertook in Tibetan lakes to improve the estimates of mid crustal strength. We also see great potential in the use of drones for detailed geodesic surveys on a regional scale. The practical application of this idea to a situation such as Uyuni has still to be tested but we believe this could be a major assistance in constructing detailed digital elevation models at a relatively low cost. Work on this project has also led us to work with a laboratory in Taiwan where U series age dating can be carried out. This technique is not generally possible within Japan and we hope to continue this collaboration in the future with its potential to develop neo tectonic studies.
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